Materials that absorb water and aqueous media, including fluids secreted or eliminated by the human body are known. These materials are generally polymers based in the form of powders, granules, microparticles, films or fibers. Upon contact with aqueous liquid systems, they swell by absorbing the liquid phase in their structure, without dissolving it. When the swelling reaches equilibrium there is obtaining a gel, which frequently is called “hydrogel”. If the water absorbency is more than 100 g water/g dried polymer the material is also called “superabsorbent” polymer.
Personal hygienic products (for example baby diapers, adult incontinence products, feminine hygiene products, and the like) are one of the highest consumers of hydrogels as superabsorbent polymers, in which the water- or aqueous media-absorbing material must have a high absorbance, both in free state and under pressure (with special reference to urine, menstrual fluid, human lactation or perspiration), to be biocompatible and to have the possibility to biodegrade. after use, by depositing the used products in landfill, which present biological activity (Bucholz F. L., Graham A. T., “Modern Superabsorbent Polymer Technology”, John Wiley & Sons Inc. 1998).
The absorbency properties of hydrogels for manufacturing personal hygienic products have been achieved by well-known methods in art.
The free absorption and absorption under pressure, at the value accepted by the producers of the personal hygienic products, have been obtained with materials (singular or composite) based on ionic or non-ionic polymers and applying different methods of synthesis and then processing. The technical solutions, with known success of market, are offered by: a) poly(acrylic acid), copolymers of acrylic acid, partially neutralized, obtained by polymerization of mono- and polyfunctional monomers, different types of composite materials included (U.S. Pat. Nos. 3,926,891; 4,090,013; 4,117,184; 4,190,562; 4,654,039; 4,666,983; 4,808,637; 4,833,222; 5,118,719; 5,567,478; 5,629,377); b) starch cross-linked by graft polymerization with acrylonitrile, bifunctional monomers of polymerization, inclusively composite materials with the participation and other natural and/or synthetic polymers (U.S. Pat. Nos. 3,935,099; 3,997,484; 4,076,663; 5,453,323; 6,107,432) and respectively c) polyacrylamide, copolymers of acrylamide and composite materials using cross-linked polymerization starting from monomers or monomers and polymers (U.S. Pat. Nos. 4,525,527; 4,654,039; 5,408,019; 5,712,316). Other materials mentioned in prior of art, with potential success techno-economic uses: copolymers of maleic anhydride and polymeric composite (U.S. Pat. Nos. 3,959,569; 3,980,663; 3,963,095; 4,389,513; 4,610,678; 4,855,179), modified celluloses (U.S. Pat. Nos. 4,959,341; 5,736,595; 5,947,031; U.S. Pat. No.), poly(vinyl alcohol) and copolymers (U.S. Pat. No. 4,124,748), polyaspartates and copolymers (U.S. Pat. Nos. 5,284,936; 5,847,013).
For the other applied domains the requirements for the absorption under load correlated with the free absorption are much less strict, and for this reason are used a large variety of imacromolecular materials (Bo J., “Study on PVA Hydrogel Crosslinked by Epiclorohydrin”, J. A. Fernandez-Nieves A., Fernandez-Barbero A., Vincent B., Nieves F. J., “Charge Controlled Swelling of Microgel Particles”, Macromolecules, 33, 2114-2118, 2000, U.S. Pat. Nos. 4,264,493, 4,349,470; 4,416,814; 5,847,089; 3,224,986; 3,926,869; U.S. Pat. Nos. RE33,997, 5,487,895; 5,549,914; 5,565,519).
It is also known that materials which correspond from the point of view of absorption don't have the capacity of biodegradation in natural media (even in the case of composites based on biopolymers, because the degree of cross-linking conferred to satisfy the absorption under load, is too high compared to the thermodynamic conditions available for the biochemical reaction of degradation) and are not recommended for absorption of menstrual fluid or human lactation because contain different chemical combinations extractable by the aqueous media mentioned, which lead directly or indirectly to the appearance of rashes, inflammation or even toxic effects (because both inadequate chemical structure of some auxiliaries used and especially the technologies of synthesis and processing applied which can not permit an advanced purification which is efficient from the economical view).
Together with the increasing of interest for the “environmental protection” concept, appears a new vision in the strategy for the obtaining of polymeric materials for consumer goods, concretized by reconsidering the signification of biodegradability.
The terms “biodegradation” and “biodegradability” although used both at the level of scientifically communication and in mass media continue to generate much confusion. This situation is due especially of interpretation more or less correctly of the definition proposed for the respective terms. Accordingly with the terminological signification proposed by Poster I. R. J. and collaborators (Foster L. J. R., Fuller R. C., Lenz R. W.—in “Hydrogels and Biodegradable Polymers for Bioapplications”, Ottenbrite R. M., Huang S. J., Park K. (Editors), ACS Symposium Series 627, American Chemical Society, Washington D.C., 1996), respectively Amass W. and collaborators (Amass W., Amass A., Tighe B.—Polymer International 47, 89, 1998) further, is presented a series of important aspects for present invention.
For purposes of this patent application, biodegradability is considered the property of a material the chemico-morphological structure of which is modified in a destructive manner (degradation), after interaction with media that contain microorganisms or biologically active combinations of substances generated by microorganisms, without participation or helped by none type of auxiliary with chemical degradation effect, which then favourize the biochemical process. The interaction mentioned represents a complex process called “biodegradation”.
As any property and in the biodegradation case must be quantified, respectively to specify its values, with the purpose of systematization of the materials between itselves and to establish the ways of amplification or diminution. The biodegradation tests can be classified having in view the following criteria: 1) the factor's type with action of biodegradation: microorganisms; enzymes; 2) the type of medium which contain factor of biodegradation; environment: soil, water and air; living organisms: human and animal bodies; 3) the parameter used to evaluate the biodegradation: structural parameters (Volke-Sepulveda T., Favela-Torres E., Manzur-Guzman A., Limon-Gonzalez M., Trejo-Quintero G.—in J. Appl. Polym. Sci., 73, (1999), 1435; Reeve M. S., McCarthy S. P., Downey M. J., Gross R. A.—in Macromolecules, 27, (1994), 825; Wool R. P., Raghavan D., Wagner G. C., Billieux S.—in J. Appl. Polym. Sci., 77, (2000), 1643; Thakore I. M., Iyer S., Desai A., Lele A., Devi S.—in J. Appl. Polum. Sci., 74, (1999), 2791; Albertsson A. C., Barenstedt C., Karlsson S., Lindberg T.—in Polymer, 36, (1995), 3075), specific for spectroscopy (FTIR, NMR, RES etc.), electronic microscopy, DSC and others; biodegradability is quantified by coefficients that express the ratio between the value of structural indicators for initial material and the one who was biodegraded; phenomenological parameters (Spence K. E, Allen A. L., Wang S., Jane J.—in “Hydrogels and Biodegradable Polymers for Bioapplications”. Ottenbrite R. M., Huang S. J., Park K. (Editors), ACS Symposium Series 627, American Chemical Society, Washington D.C. 1996), when the biodegradability is quantified by: weight loss, modification of the mechanical (rheological) properties' value, O2 consumption, evolution of CO2 emission; 4) the scale at which is made the biodegradation's experiment: laboratory (in vitro), effectuated with demonstrative purpose for a polymeric structure given, in principal with enzyme, with different specificities versus the support used, when the quantification is done both with structural parameters and phenomenological parameters (especially with by the weight loss and of the rheological properties' modification); it is used also the incubation in media with cells and/or microorganisms, respectively pilot scale.
The most controversial aspect of the biodegradation tests is referred at the manner in which these can offer information that correspond the criteria imposed by the environmental protection legislation. In this sense, it is considered that the biodegradation process can generate three different levels of structure's modification of a substance (Perrone C.—Poliplasti 398/399—january/february 1991, 66): a) primary biodegradation, characterized through that it is alter only a part from chemical structure, that means it is maintain the principal chain of the polymer and it is modified only some functional groups. In fact, the material maintain its volume, eventually the mass too but it can't be identified by specifically physico-chemical methods; b) partial biodegradation, characterized through that it is loosed the material integrity of substance, carried out by fragmentation of the volume in the same time with disappearance of an appreciable mass from the initial one. In facts from the material entity remain in the biological medium only secondary products, in gaseous, liquid or solid state (that can be in their turn pollutant factors); c) complete biodegradation, characterized through that the initial material entity disappears from biological medium as a result of the advanced fragmentation of molecules followed by the favoring of complete chemical degradation or/and their digestion by the microorganisms.
In accordance with what was mentioned above, in the prior of art there are known hydrogels, including superabsorbent polymers, which are purported to be biodegradable: (U.S. Pat. Nos. 4,944,734; 4,952,550; 4,959,341; 5,190,533; 5,417,997; 6,444,653), but in all cases the absorbency is inferior versus the traditional synthetic materials.
In our previous U.S. Patent Application, Pub. No: US 2002/0193516 A1, filed Mar. 30, 2001, is discussed about a biocompatible, biodegradable material water absorbent, with adequate absorbency, but which uses a method of synthesis and processing where is utilized organic solvents, that lead to high cost of production, because of the supplementary operation necessary for product purification and the technological effluents cleaning.
Biocompatibility is accepted to be a notion by whom is understanding a sum of biochemical characteristics which a material possess that make to be accepted by the living organisms (human, animals and plants), as an integral part of them, without resulting in spontaneous or in time the manifestation of a repulsive or toxical phenomenon in the form of inflammation, infections and others (Black J., “Biological Performance of Materials: Fundamentals of Biocompatibility”, 2d ed. M. Dekker, N.Y., 1992).
The standards that have guided biocompatibility testing are the Tripartite Guidance; the International Organization for Standardization (ISO) 10993 standards, which are known as the Biological Evaluation of Medical Devices and remain under development internationally; and FDA blue book memorandum.
In accordance with the foregoing, a material is more biocompatible with a living organism the more similar the material to the organism's own biopolymers with which the material comes into contact. Thus, water- and aqueous media-absorbent materials presently known having advanced biocompatibility (even totally) intended to be in contact with human body are those that contain collagenic biopolymers: native collagen, solubilized collagen, gelatin and even collagen hydrolysate (Hoffman A. S., Daly C. H., “Biology of Collagen”, Viidik Vunst J. Eds., Academic Press, New York, 1980; Ward A. G., Courts A., “The Science and Technology of Gelatin”, Academic Press N.Y., 1977 and U.S. Pat. Nos. 5,376,375; 5,292,802; 5,945,101; 6,071,447 and others).